Analysis of polycyclic aromatic hydrocarbons
Polycyclic
aromatic hydrocarbons, PAHs, are among the most studied contaminants in
different matrices, since many of them are considered potentially
carcinogenic.
The determination of PAHs is a great challenge for
analytics. One reason for this is the large number of possible food
matrices. In addition, laboratories have to meet requirements such as
reducing turnaround time without compromising analytical parameters such
as sensitivity, precision and accuracy. As a result, highly automated
analytical procedures are required for the analysis.
Pitfall sample preparation
All
samples must be prepared before the actual measurement. Depending on
the sample matrix, this is easier or more complex. Due to the necessary
sensitivity, a high quantity of food sample must be used from which the
PAHs must be extracted. However, care must be taken not to extract other
substances in addition to PAHs, which could falsify the analysis or, in
the worst case, damage the expensive analytical equipment.
The
ideal basis for the determination of PAHs is the CHRONECT LC-GC
technology by Axel Semrau, which has been established in the routine
analysis of food for several years. For this application an
LC-LC-GC-MS(/MS) solution and the imPAHct method were developed: innovative multidimensional PAH cleanup technology.
Manual
sample preparation and associated pitfalls can be reduced to a minimum
by this application. The figure shows the sample preparation procedure
with this application depending on the food group. Edible oils can
usually be injected directly after dilution, while other food groups are
prepared in only 10-15 minutes.
Methodology
To
determine PAHs, a simple and fast extraction of the sample is
performed. The extract is purified after a short manual processing in
Axel Semrau's LC-GC system by a two-stage LC separation (LC-LC-Cleanup).
After injection of the sample by the xyz robot CHRONECT Robotic,
the sample is freed from all substances that are more polar than PAHs. A
bare silica gel column in normal phase HPLC mode is used for this
purpose.
However, the purified PAH fraction still contains
numerous interfering substances that have to be separated by means of a
second LC dimension. A so-called π donor-acceptor chromatography is used
for this purpose, which can selectively enrich π electron-rich
substances. The resulting PAH-rich sample extract is then transferred to
the gas chromatograph as described above and separated, detected and
quantified using classical GC-MS(/MS) analysis.
Fast results and low detection limits
This
intelligent matrix management makes it possible to determine the PAHs
prescribed by the EFSA for analysis fully automatically. Depending on
the detector, detection limits are achieved that are lower by a factor
of 100 than the prescribed European limits for infant food.
The final sample result is available after 45 minutes after the sample has been placed in the system.
System structure
The
system already successfully uses classic assemblies from Agilent and
Shimadzu. It is also possible to use other GC-MS systems, such as those
from Bruker or others. The control software CHRONOS
is the core of the control and combination of the individual modules.
In combination with the LC-GC interface, CHRONOS coordinates all
subsystems so that they perform the right action at the right time -
independent of the data system of the individual equipment
manufacturers.
Commissioning
Axel Semrau's LC-GC solutions
are pre-installed and tested in a Factory Acceptance Test in the
application laboratory. They are delivered to the user ready for use and
are checked again there within the scope of a Site Acceptance Test.
This ensures the fastest possible start of routine measurement
operations.
Practice-oriented application
Marco Nestola was awarded the Ernst Bayer Prize
in 2016 for his publication on this separation technology. In the same
year, this application also made it onto the Application Award
shortlist. With this prize, the German specialist magazine Laborpraxis
at analytica honors practical and innovative applications.